Fuse link construction



S. l. LINDELL FUSE LINK CONSTRUCTION Feb. 3, 1959 Filed Aug. '7, 1956 INVENTOR. ,gzzrdZZL/Zde/J,

i W m 2 w d J We 5 MM FUSE LNK CONSTRUCTION Sigurd l. Linrleil, Chicago, lli., assigner to S e C Electric Company, (hicago, lil., a corporation of Delaware Application August 7, 1956, Serial No. 602,666

Ciaims. (Cl. 20G- 121) This invention relates, generally, to fuses for high voltage electric circuits and it has particular relation to fuse links therefor. lt constitutes an improvement over the fuse link construction shown in U. S. Patent No. 2,253,720, issued August 26, 1941.

Among the objects of this invention are: To provide an improved indicator type of fuse link in which a reliable indication of fuse link operation is provided when it blows at various current levels; to insure complete removal of a portion of the fuse link and the indicator following blowing of the fuse link in any current range; to provide a rigid connection between the fusible element and the indicator; and to mechanically and electrically interconnect a terminal fitting on the indicator with an end of a rigid fuse link terminal.

Other objects of this invention will, in part, be obvious and in part appear hereinafter.

This invention is disclosed in the embodiment thereof shown in the accompanying drawing and it comprises the features of construction, combination of elements and arrangement of parts which will be exemplified in the construction hereinafter set forth and the scope of the application of which will be indicated in the appended claims.

For a more complete understanding of the nature and scope of this invention, reference can be had to the following detailed description, taken together with the accompanying drawing, in which:

Figure l is a view, in side elevation, showing a bayonet type of fuse device with which the present invention is adapted particularly for use;

Figure 2 is a vertical sectional View, at an enlarged scale, of the bayonet portion of the circuit interrupter shown in Figure l;

Figure 3 is a vertical sectional View, at an enlarged scale, of the fuse link shown in Figure 2;

Figure 4 is a horizontal sectional View, taken generally along the line ft-d of Figure 3 and showing the relationship of the parts before they are deformed;

Figure 5 is a sectional view, at an enlarged scale, through a portion of a die that is employed for deforming portions of the parts to be interconnected; v

Figure 6 is a view, partly in side elevation and partly in section, of the metallic terminal tting and the indicator rod of insulating material molded in place thereon; and

Figure 7 is an elevational View of the fitting interconnecting the lower end of the rod-like terminal and the upper end of the indicator rod, taken at right angles to the showing in Figure 2.

Referring now particularly to Figure l of the drawing, it will be observed that the reference character 10 designates a cross arm having a clamp 11 secured thereto to which a bracket 12 can he attached that supports an insulating housing 13 of a bayonet type fuse circuit interrupter that is shown, generally, at 14. The circuit interrupter 1d preferably is of the type shown in U. S.

arent Patented 3,

Patent No. 2,591,949, issued April 8, 1952. At its upper end the housing 13 has an insulating handle 15.

Referring now to Figure 2 of the drawing, it will be observed that the reference character 16 designates an upper terminal which is threaded into the handle 15 of the circuit interrupter 14. The terminal 16 is the upper terminal of a fuse tube 17 which extends into the housing 13 and has a lower terminal 18 that preferably is constructed as shown in application Serial No. 535,683, tiled September 2l, 1955, now Patent No. 2,806,919, issued September 17, 1957. The lower terminal 18 has a depending tongue 19 which is provided with a tubular extension 20 at its lower end that is open on one side and has a longitudinal slot 21 therein which is generally aligned with the longitudinal axis of the fuse tube 17. The width of the slot 21 is indicated at 22 and is of irnportance in connection with the construction of the fuse link to be described presently. At its lower end the slot 21 has a tapered terminal seat or shoulder 23 that faces generally downwardly.

Provision is made for interconnecting the upper and lower terminals 16 and 18. For this purpose a button head 25 is employed to engage the upper end of the upper terminal 16 and it has depending therefrom a coil tension spring 26 and a flexible cable 27 therein. At their lower ends the spring 26 and cable 27 are secured to an internally threaded terminal 28.

Detachably secured to the terminal 2S is a replaceable indicating fuse link that is indicated, generally, at 29. It is employed for interconnecting the terminal 23 with the lower fuse tube terminal 18.

As illustrated more clearly in Figure 3 the fuse link 29 is provided with an upper terminal 30 which has a threaded portion 31 to interlit with the threaded portion of the terminal 28. The terminal 3i) has a fuse element receiving portion 32 to which a helical fusible element 33 and a strain element 34 are secured. The fusible element 33 may be formed of pure silver wire. lt may be formed of other materials, such as tin, as disclosed in U. S. Patent No. 2,253,720, issued August 26, 1941, in which case it takes the form of a rod or sleeve of tin as may be desired. When the fusible element 33 of silver and the strain element 34 are employed, as shown in Figure 3, their upper ends are inserted in a longitudinal aperture 35' that is provided in the portion 32 and then the opposite sides are deformed, as indicated at 36, to mechanically secure these ends in electrical and mechanical engagement with the upper terminal 30. Surrounding the fusible element 33 and strain element 34 is au insulating sleeve 37 which is telescoped over the portion 32 of the upper terminal 34) and secured thereto by a suitable adhesive.

The lower ends lof the fusible element 33 and strain element 34 are mechanically secured to a rodlike lower terminal 38 in the form of a silver plated copper rod. These lower ends are positioned in a longitudinal aperture 39 in the upper end of the terminal 38 and then the opposite sides are deformed as indicated at di) to provide the desired mechanical and electrical connection.

The rod-like lower terminal 3S projects out of the lower end of the insulating sleeve 37 and its lower end 41 is counterbored to provide a hollow construction as indicated at 42. The lower end [t1 interfits with a hollow sleeve i3 which constitutes the upper end of a brass fitting 44 that preferably is silver plated. The brass fitting 44 is mechanically and electrically secured to the lower end 41 of the rod-like lower terminal 38 and it has an upwardly facing shoulder 45 for engaging the shoulder 23 on the tubular extension 20 to hold the spring 26 under tension as shown in Figure 2.

Depending from the brass fitting d4 is a knurled insert 45 and around it is molded an indicator rod 47 that is formed of a suitable plastic material having insulating characteristics. At its lower end the indicator rod 47 is provided with annular ridges 4% which facilitate gripping the same for tensioning the spring 26 and extending it suliiciently to engage the shoulder i5 of the fitting da with the shoulder 23 of the extension 2@ of the fuse tube terminal i8.

Since a substantial amount of heat may be generated on iiow of load current through the fitting 44%-, particular care is taken in choosing the material for the rod 47. Preferably it is formed of a polyamide, such as nylon, which is resistant to heat distortion up to about 250 F. and yet can be economically manufactured.V ThisV material is capable of withstanding, without softening, heat incident to high ambient temperature and full load or overload of theV circuit interrupter i4.

lit will be observed that the upper end of the fitting 4d, as shown in Figure 6, is counterbored to provide the hollow portion i9 whose diameter is such as to freely receive the lower end il of the rod-like terminal V3:8' in the relationship shown more clearly in Figure 4. The telescoped parts then are positioned in a die 52, Figure 5, which has an opening 53 the width of which is less than one-half of the internal circumference of the bore d2 in the lower end al plus twice the sum of the wall thicknesses of the lower end il and of the hollow sleeve portion Then a punch 542- is caused to enter the opening 53 to deform the parts and provide intimate electrical and mechanical engagement therebetween. Since the parts are confined in the opening 53 in the die 52, high pressure is set up along the sides of the joined parts as they are deformed and cold worked and this assures good permanent electrical contact therebetween. Any tendency for the hollow sleeve to spring back to its original shape increases the edge pressure onV the iiattened portion of the lower end il and thus automatically increases the pressure applied thereto.

lt will be understood that the punch 5d engages only a portion of the hollow sleeve d3 with the result that the extreme end 55 of the lower end l is not deformed nor is the overlying portion of the hollow sleeve d3 flattened to the extent that the remaining portion is. Accordingly, a shoulder 56 is formed on the extreme lower end 55 which bears against a correspondingly shaped shoulder 57 at the base of the hollow sleeve d3. This construction is capable of resisting any tension or pull likely to be applied to the rod-like lower terminal and to the litting la tending to separate them.

The total thickness or dimension of the deformed parts, as indicated at 58 in Figure in the direction of the width 22 of the slot 2l is such as to permit them to intert readily in the longitudinal slot 2li. ln other words, the thickness 5S is substantially less than the width 22 of the slot 21 so that, when the fusible element 33 and strain element 3d blow, the deformed portion 43. of the fitting la can fall freely through the slot 2l. under the influence of gravity.

rlhe maximum transverse dimension 5 of the rod-like lower terminal 3e is about Athe same as the dimension 5S and is substantially less than the width 22 of the slotZl. Likewise, the outside diameter of the helix of the fusible element 33, as indicated at dit, is about tne same as the dimension S or smaller so that, in the event they fuse link operates on a low current fault and the lowerA portion of the fusible element 33 remains, it will fall freely through the slot 2l.

lt is advantageous to employ the lower terminal 33 for interconnecting the fusible element 33 and strain element 3e with the iitting 44 and to form it throughout its entirety as a rod-like member rather than to form it of flexible material, such as a flexible lead, as shown, for example in application Serial No. 465,922,'led November 1, 1954, now Patent No. 2,813,952, issued November i9, i957. This is particularly true when the trailer confi struction shown in that application is employed. When the trailer construction is used, a nut is threaded on the tubular extension 2G and there is the possibility that, if a flexible lead is employed, it may be bent readily by expulsion forces or gas blast and overlie or hook around the nut and tend to prevent any substantial movement of the indicator rod 47 downwardly. By employing the rodlike lower terminal 3S and providing a construction such that all parts, which are intended to fall out on operation of the device, have a maximum transverse dimension in the direction or the width 22 of the slot 21 less than the width of this slot, the movement of the indicator rod 47 entirely from the circuit interruptor 14 is insured. This is true for all ranges of operation of the device. For example, when the device operates on a slight overload and only a portion of the fusible element 33 is fused out, the weight of the rod-like terminal 3S and of the indicator 47 is such that the assembly falls freely through the slot 2l to the ground. At the` other end of the range of operation where the device is called upon to interrupt an extremely heavy overload, a substantial expulsion `action takes place within the fuse tube i7 resulting in the destruction ofthe insulating sleeve 37 and the propelling of the rod-like lower terminal 33 outwardly together with the. insulating rod 47. At either end of the range of operation, because the width 22 of the slot 21 is such that the lower terminal 2S can move freely therethrough and since the terminal 36 is rod-like in character and is unlikely to bend, positive movement of the indicator rod 47 away from the interrupter 14 is always assured. The lineman, then noting the absence of the indicator rod 47, is advised at once that the particular circuit interrupter under consideration has operated and he can then take the necessary steps for replacing the fuse link 29 to restore service.

Since certain further changes can be made in the foregoing construction and different embodiments of the invention can be made without departing from the spirit and scope thereof, it is intended that all matter shown in the accompanying drawing and described hereinbefore shall be interpreted as illustrative and not in a limiting sense.

What is claimed as new is:

l. A fuse comprising, in combination, a fuse tube having terminals at its ends, onek of said terminals having a longitudinal slot spaced from said fuse tube and extending generally along a projection of its longitudinal axis, and means interconnecting said terminalsfincluding a fuse link having terminals connected respectively to said fuse tube terminals and interconnected by fusible means, the fuse link terminal connected to said one fuse tube terminal being rod-like throughout its entirety and extending through said'slot and having a shoulder at its outer end bearing against the outer ends of the sides of said slot, thatV portion of said rod-like terminal extending through said slot being flattened and terminating in said shoulder.

2. A fuse comprising, in combination, a fuse tube having terminals at its ends, one of said terminals having a longitudinal slot spaced from said fuse tube and extending generally along a projectionof its longitudinal axis, and means interconnecting said terminals including a fuse link having terminals connected respectively to said fusetube terminals and interconnected by fusible means, the fuse link terminal connected to said one'fuse tube terminal being rod-like throughout its entirety and extending into said slot at its outer end, said outer end being hollow, and a fitting having a hollow portion telescoped with said hollow outer end and a shoulder bearing against the outer ends of the sides of said slot, the telescoped portions of said outer end and of said titting being conjointiy deformed to provide a mechanical connection therebetween.

3. A fuse comprising, in combination, a fuse tube having terminals at its ends, one of said terminals having a longitudinal slot spaced from said fuse tube and extending generally along a projection of its longitudinal axis, and means interconnecting said terminals including afuse link having terminals connected respectively to said fuse tube terminals and interconnected by fusible means, the fuse link terminal connected to said one fuse tube terminal being rod-like throughout its entirety and extending into said slot at its outer end, said outer end being hollow, and a fitting having a hollow portion telescoped over said hollow outer end and a shoulder bearing against the outer ends of the sides of said slot, the telescoped portions of said outer end and of said fitting being conjointly deformed to provide a mechanical connection therebetween, said hollow portion of said outer end of said rod-like terminal being deformed in predetermined spaced relation from its outer end which is substantially undeformed and provides a head reacting against an inner shoulder on the inside of said hollow portion of said fitting.

4. Means for interconnecting the terminals of a fuse tube one of which has a longitudinal slot spaced from the fuse tube and extending generally along a projection of its longitudinal axis, said means including a fuse link having terminals for connection respectively to said fuse tube terminals and interconnected by fusible means, the fuse link terminal for connection to said one fuse tube terminal being rigid throughout its entirety and arranged at one end to extend through said slot and having a shoulder at its outer end for bearing against the outer ends of the sides of said slot, that portion of said rigid terminal extending through said slot being attened and terminating in said shoulder.

5. Means for interconnecting the terminals of a fuse tube one of which has a longitudinal slot spaced from the fuse tube and extending generally along a projection of its longitudinal axis, said means including a fuse link having terminals for connection respectively to said fuse tube terminals and interconnected by fusible means, an insulating sleeve secured at one end to one fuse link terminal and extending over said fusible means and the other fuse link terminal, said other fuse link terminal being rod-like throughout its entirety and extending out of the other end of said insulating sleeve and arranged at its outer end to extend through said slot, said outer end being hollow, and a fitting having a hollow portion telescoped with said hollow outer end and a shoulder for bearing against the outer ends of the sides of said slot, the maximum transverse dimension of said shoulder not exceeding the outside diameter of said insulating sleeve, the telescoped portions of said outer end and of said tting being conjointly deformed to provide a mechanical connection therebetween.

References Cited in the le of this patent UNITED STATES PATENTS 1,782,089 Baumer Nov. 18, 1930 2,011,449 Kerr Aug. 13, 1935 2,429,527 Schultz Oct. 2l, 1947 2,662,139 Lindell et al. Dec. 8, 1953 2,793,267 Mikos May 21, 1957 2,806,919 Conrad Sept. 17, 1957 2,813,952 Baker et al. Nov. 19, 1957 FOREIGN PATENTS 596,202 Germany Apr. 28, 1934 

